The present invention relates to a method and apparatus for monitoring the electrical and optical performance of one or more field emission display (FED) devices during a burn-in period. More specifically the video driver circuitry, the field emission tips and the phosphor screen of such devices all require testing and burn-in prior to sale for the purpose of obtaining proper steady state operation, detecting faults in parts which may fail prematurely and for diagnostic purposes.
Known techniques in the manufacture of semiconductor devices involve the burning in of such devices in order to accelerate the failure of those devices having defects. Such testing is conventionally performed at elevated temperatures.
Additionally, image display devices such as cathode ray tubes, although known to have good characteristics with respect to color, brightness, contrast and resolution, use phosphors which generally degrade in performance upon initial use under prolonged cathode ray excitation. Thus, the phosphors are generally aged until stable luminance conditions are obtained along with a uniform screen appearance. Although cathode ray tube technology has been applied in various applications including desktop computer screens with good results, such devices are bulky and consume relatively large amounts of power.
More recently flat panel displays have become increasingly important in a variety of applications where lightweight portable screens with good display characteristics are required. One type of flat panel display device which is well suited for such applications is the thin film field emission display device. Such flat panel displays seek to combine the cathodoluminescent-phosphor technology of cathode ray tubes with integrated circuit technology to obtain thin high resolution displays wherein each pixel is activated by its own electron emitter or set of emitters. Such field emission displays in elementary form include a generally planar substrate having an array of integral projecting emitters which are typically conical projections grouped into emitter sets. Depending upon the size and type of display, a conductive extraction grid is positioned above the emitters and driven at a positive voltage with the emitters selectively activated by providing a current path to ground with appropriate voltage differential between the emitters and extraction grid. The resulting electric field extracts electrons from the emitters. Moreover, the field emission display device additionally includes a display screen-anode formed from a glass plate coated with a transparent conductive material forming a relatively high positive voltage differential with respect to the cathode emitters. The display screen additionally includes a cathodoluminescent layer covering the conductive anode surface whereby emitted electrons are attracted by the anode and strike the phosphor layer to thus cause the emission of light at the impact site which in turn passes through the anode and glass plate.
The luminescent level of the produced light is dependent upon the magnitude of the current flow to the emitters which is selectively controlled to produce a desired image. Field emission devices and various manners of driving circuits for use therein are known in the art, examples of which are found in commonly assigned U.S. Pat. No. 5,357,172 issued Oct. 18, 1994 to Lee et al, U.S. Pat. No. 5,387,844 issued Feb. 7, 1995 to Browning and U.S. Pat. No. 5,459,480 issued Oct. 17, 1995 to Browning et al. These patents are hereby incorporated by reference in their entirety.
In the operation of such field emission display devices there is a relatively high voltage differential generally above 200 volts between the cathode emitters and the display screen, and it is important to prevent electrical breakdown between the cathode electron emitting surface and the anode or extraction grid by maintaining an evacuated cavity between the emitters, the extraction grid and the anode. However, it is additionally desired to maintain relatively narrow spacings to obtain structurally thin flat panel displays. Moreover, since the manufacture of FEDs is relatively recent, methods and apparatus for continual monitoring of the electrical and optical performance of such displays are unknown.
Accordingly, a primary object of the present disclosure is that of providing a practical method and apparatus whereby the video driver circuitry, the field emission tips and the phosphor screen included in field emission display devices can be appropriately tested for electrical and optical performance during burn-in before the displays are sold or incorporated in a variety of applications.